[Dave in MN]

I have a 1.5" bar on my line boring machine. Given its diameter, I use it only for boring blocks for insert bearings. Even with the increased diameter, it will chatter when cutting the thrust washer pockets.
I remove the rear cap when boring for the half circle front thrust. The cutter leaving the surface of the cut for half of the rotation and then coming into contact creates a bit of loud "clack" noise but with a slow feed, it works.
Like Jim, full 360 thrust at rear and 1/2 thrust at the front of the rear bearing. I cut the thrust pocket in the block and retain it with an uncut cap.
Good Day!